Connector assembly for an implantable medical device and process for making

ABSTRACT

A connector circuit assembly for use in an implantable medical device, and a method of making the assembly that includes a core portion formed of a thermoplastic material using either an injection molding process or a machining process. This core portion is adapted to be fitted with at least one electrically-conductive circuit component such as a connector member, a set-screw block, or a conductive jumper member. In one embodiment of the invention, the core portion includes multiple receptacles or other spaces that are adapted to be loaded with the various circuit components. The core assembly is positioned into a second-shot mold assembly, and a second thermoplastic material is injected into the mold so that the second thermoplastic material extends over and adheres to the core portion and the circuit component.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/612,278 filed on Dec. 18, 2006, entitled “CONNECTOR ASSEMBLY FOR ANIMPLANTABLE MEDICAL DEVICE AND PROCESS FOR MAKING”, to Zart et al.,which is a continuation of U.S. patent application Ser. No. 10/966,636,filed on Oct. 15, 2004, entitled “CONNECTOR ASSEMBLY FOR AN IMPLANTABLEMEDICAL DEVICE AND PROCESS FOR MAKING”, now U.S. Pat. No. 7,175,482,which is a divisional of U.S. patent application Ser. No. 09/885,354,filed on Jun. 20, 2001, entitled “CONNECTOR ASSEMBLY FOR AN IMPLANTABLEMEDICAL DEVICE AND PROCESS FOR MAKING”, now U.S. Pat. No. 6,817,905,which claims priority to U.S. Provisional Application No. 60/212,746,filed on Jun. 20, 2000 incorporated herein by reference in theirentireties.

FIELD OF THE INVENTION

This invention relates to a process for molding a circuit component; andmore particularly, to a two-shot thermoplastic molding process formanufacturing an electrical connector.

BACKGROUND OF THE INVENTION

Electrical connectors and other similar electrical components ofteninclude electrical conductors embedded within an insulating housing toisolate the conductor from the surrounding environment. Embedding theconductor within a housing protects the conductor from damage, and alsoprevents the delivery of an electrical shock. Electrical isolation isparticularly important when the connector is to be coupled to animplantable medical device such as a pacemaker or defibrillation system.

One way to form an electrical connector having conductors embeddedtherein is to mold a solid set-screw block using injection moldingtechniques. After the molding is completed, the surface of the set-screwblock is formed to include channels. Wires or other types of connectorsare pressed into the channels. Generally, each end of each wire iswelded to some type of electrical contact. An insulating adhesive isthen applied over the wires and channels. If the connector is to be usedwith an implantable medical device, a medical adhesive is often employedfor this purpose. The adhesive is cured to form a protective, insulatinglayer that isolates the wires from external elements.

Although the afore-mentioned method is relatively straight-forward, itrequires manual application of the adhesive. This introduces variablesinto the manufacturing process. If the adhesive is not properlydispensed, some portions of the conductor may become exposed. As aresult, shorts may develop between adjacent conductors. Additionally, aconductor may come in contact with external elements, causingdegradation and loss of conductive capabilities. Moreover, because amanual process is employed, the manufacturing mechanism is moretime-consuming and expensive.

An alternative approach to the use of adhesives involves the positioningof one or more conductors within a mold in some predeterminedorientation. An insulating plastic is then introduced into the mold toencapsulate the conductors. The plastic hardens to provide the necessaryinsulating layer around the conductors. While this process eliminatesthe variables associated with a manual step, it is neverthelessdifficult to implement with other than a simple design. This is becausethe introduction of the plastic into the mold at high pressuresgenerally causes the position of the conductors to shift. This mayresult in shorts between multiple conductors, or conversely, may resultin loss of a desired electrical connection. While plastic injectionsystems of this nature generally include mechanisms to hold theconductors in place during the injection process, the process is moreprone to failure than other methods because shifting of components mayoccur regardless of the efforts to prevent it. Additionally, a morecomplex tooling system is required to implement the process. Finally,the difficulty associated with maintaining isolation between multipleconductors places limits on the assembly dimensions. That is, anassembly cannot be made too small because shorts will occur betweenclosely spaced conductors that shift during the mold injection process.

Yet another approach used to create connector assembly includes use of atwo-step thermoset casting process. A first mold is used to receive athermoset plastic material such as an epoxy. As is known in the art, athermoset plastic hardens because of a chemical reaction occurringbetween the various components of the plastic material. After the curingprocess is complete, the first molded connector element is removed fromthe mold. Conductors are selectively positioned on the exterior of thisfirst element. The first element is then positioned within a second moldand a thermoset material is selectively applied to the first element toencapsulate the conductors.

The two-step thermoset process provides a mechanism for embeddingconductors within a connector in a more precise manner. This is becausethe first element holds the conductors in position while the secondmolding step is performed. However, because thermoset material requiresa relatively long time to cure, the process is slow. The manufacturetime is increased since two serial curing steps are required. Moreover,because the final products may not be removed from the molds until thecuring is completed, many molds must be employed to increase output.

What is needed, therefore, is an improved mechanism for creating morecomplex connector structures using a faster production cycle.

SUMMARY OF THE INVENTION

The current invention provides an improved circuit assembly for use inan implantable medical device, and a method of making the assembly. Thecircuit assembly includes a core portion formed of a thermoplasticmaterial using either an injection molding process or a machiningprocess. This core portion is adapted to be fitted with at least oneelectrically conductive circuit component such as a connector member, aset-screw block, or a conductive jumper member. In one embodiment of theinvention, the core portion includes multiple receptacles or otherspaces that are adapted to be loaded with the various circuitcomponents. Core portion may further be provided with groove and ridgemembers designed to position and retain conductive jumper members atpredetermined locations at the surface of the core portion. Suchconductive jumpers may be welded or soldered to a respective one ofthese circuit components to form electrical contacts between the jumpersand the respective circuit component.

After the electrically conductive circuit components are positioned inthis manner with respect to the core portion, this core assembly isprepared for an overmolding process. This involves ensuring that certainportions of the core assembly will be protected from the flow ofthermoplastic material during a subsequent overmold process. Thisprocess may include loading bushings into various connector membersand/or set-screw blocks of the core element assembly.

When the core assembly has been prepared for the overmolding process, itis loaded into a second-shot mold. In one embodiment of the invention,the core assembly is aligned and retained within a cavity of the mold byutilizing slidable members that are provided by the mold, and that areadapted to engage the core assembly. Positioning of the core assemblywithin the mold cavity may further be accomplished using pegs that areadapted to engage various corresponding apertures of the core elementassembly.

During the overmold process, a second-shot of thermoplastic material isinjected into the mold. This thermoplastic material is heated to atemperature at, or above, the melting point of the material. Thisthermoplastic material is hot enough to create a bond between the coreportion and the overmold material. To achieve this, the mass of the coreelement as compared to that of the overmold material is made as small aspossible so that the heat energy from the mold is able to adequatelyheat the core portion. In one embodiment, the mass of the core portionis less than fifty percent of the mass of the overmold material, andpreferably is less than thirty percent. Bonding may further be enhancedby providing ridges on the surface of the core portion that are meltedduring the overmold process and thereafter integrated with the overmoldmaterial. The bonding may also be facilitated by pre-heating the coreportion prior to injecting the second shot of thermoplastic materialinto the mold.

In one embodiment of the invention, a hermetically-sealed connectorassembly is provided for use with an implantable medical device (IMD)such as a cardioverter/defibrillator, a pacemaker, or any other type IMDthat is adapted to coupled to medical electrical leads. Because theconnector assembly is manufactured using thermoplastic materials, themanufacturing process may be completed in a much shorter amount of timethan similar assemblies formed of thermoset materials. The connectorassembly includes one or more connectors that are adapted to couplemechanically and/or electrically to the pin or ring connectors of amedical electrical lead. Such connector members may conform to variousstandards for medical electrical leads, such as IS-1 and DF-1 standards.

Other aspects and advantages of the current inventive circuit assemblysystem and method of making the circuit assembly system will be apparentfrom the drawings and accompanying detailed description of the inventionembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of a connector core element of oneembodiment of the current invention.

FIG. 2 is a front perspective view of a core member loaded withrespective set-screw blocks and connector members.

FIG. 3 is a back perspective view of an alternative embodiment of thecore member.

FIG. 4 is a bottom perspective view of core member.

FIG. 5 is side perspective view of an alternative embodiment of thecircuit member.

FIG. 6 is side perspective view of an alternative embodiment of the coreelement adapted to engage the circuit member of FIG. 5.

FIG. 7 is a side perspective view of circuit member positioned on thesurface of core element.

FIG. 8 is a front perspective view of an exemplary lead core assembly.

FIG. 9 is a perspective view of a core element being prepared for theovermolding process.

FIG. 10 is a side perspective view of an alternative embodiment of acore element which is designed to minimize core element mass.

FIG. 11 is a perspective side view of an exemplary connector assemblyformed after injection of the second-shot material.

FIG. 12 is an alternative embodiment of the second-shot mold assembly ofFIG. 9.

FIG. 13 is a flowchart of the inventive assembly process.

FIG. 14 is a side perspective view of a completed connector assemblycoupled to an implantable medical device (IMD).

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a front perspective view of a connector core element 2 of oneembodiment of the current invention. Core element is integrally formedof a biocompatible thermoplastic material, which may be a polyurethanesuch as pellathane commercially available from The Polymer TechnologyGroup (PTG) Incorporated, or Tecothane® commercially available fromThermedics Incorporated. Other polyurethane materials are suitable foruse in the current inventive process, as are other thermoplasticmaterials such as polysulfone. In one embodiment, a suitablebiocompatible polyurethane may have a hardness of between 50D and 90D(Shore), and is preferably about 75D.

The core element 2 is formed by heating the thermoplastic material to atemperature that is at, or slightly above, the melt point. The materialis then injected into a primary mold formed into the desired shape ofthe core element and allowed to cool. Cooling is generally completed inbetween twenty to seventy seconds. This is much shorter than the curingperiod for thermoset materials, which may be as much as one hour. Aftercooling, core element 2 is removed from the mold. The removal processinvolves opening the mold, which includes an ejection mechanism thatautomatically releases the core element.

Core element 2 may take many different shapes. In one embodiment, coreelement includes a structure that supports various metal piece parts ina stable manner that can be maintained during a second-shot moldingprocess to be discussed below. In the embodiment of FIG. 1, core element2 includes receptacles 4, 6, and 8. Each of the receptacles is adaptedto receive a respective set-screw block, such as set-screw block 10 tobe inserted within receptacle 6, and 12 to be inserted within receptacle8. Receptacle 4 is adapted to receive a similar set-screw block notshown in FIG. 1 for purposes of simplification. Set-screw blocks may beformed entirely, or partially, from a conductive material such as MP35N,stainless steel or titanium.

The set-screw blocks are loosely maintained within a respectivereceptacle by the shape of core element 2 until the second-shotover-molding process is completed. Each of these set-screw blocksincludes an opening such as opening 16 to receive a set screw, and asecond opening such as opening 17 to receive the pin or ring connectorprovided at the proximal end of a medical lead. A set screw insertedwithin opening 16 is used to mechanically couple to a lead connector pinor ring to hold the lead in place, as will be described further below.

In an alternative embodiment, the various receptacles needs not beincluded and the set-screw blocks may be integrally formed within thecore element by positioning the set-screw blocks with the primary moldprior to injecting the thermoplastic material to form core element 2. Inthis instance, sealing means must be provided to prevent thethermoplastic from being injected into the openings of the set-screwblocks. For example, the primary mold could include peg members adaptedto be loaded into the openings of set-screw blocks so that a tight sealis formed prior to injecting the thermoplastic into the mold. The pegswould also retain the set-screw blocks in position during thehigh-pressure injection process. Because of the complications associatedwith maintaining the set-screw blocks in position during the injectionprocess, the former embodiment is preferred.

Returning to FIG. 1, the exemplary embodiment of core element 2 alsoincludes additional circular receptacles 24 and 26. Each circularreceptacle includes an aperture 25 and 27, respectively, to receive theconnector pin of a medical electrical lead. For example, during use, alead connector pin may be inserted within aperture 27 and furtherthrough opening 17. The lead is held in place by a fastening memberinserted within opening 16 of set-screw block 10 and tightened on thelead pin or ring as is known in the art.

In the embodiment shown, each circular receptacle 24 and 26 is adaptedto receive a respective connector member such as connector member 30.This type of connector member may be formed entirely or partially of aconductive material such as stainless steel or titanium. Connectormember 30 is shown to include a multi-beam connector (MBC) 32 adapted tocouple electrically and mechanically to a ring connector of a bipolarmedical electrical lead. This type of connector member would support alead having a connector conforming to the IS-1 standard, for example.Other types of connector members may be utilized to form an electricaland/or mechanical connection, as is known in the art.

In an alternative embodiment, the connector members may be eliminated byintegrally forming the connectors such as connector member 30 withincore element 2. This may be accomplished by loading the primary moldwith the connectors prior to injecting the thermoplastic. As discussedabove with respective to the set-screw blocks, some mechanism must beprovided to prevent the thermoplastic from flowing over the conductivesurface of the connectors. Additionally, the connector members must beretained in position during the high-pressure injection process. Becauseof the additional complexity associated with the need to maintain thesecomponents in position, the former embodiment of inserting thesecomponents into the completed core element 2 is preferred.

Core element 2 further includes additional lead bores 28 and 29 toreceive the connector pins of additional leads. These lead bores may beadapted to couple to the pin of a lead conforming to the DF-1 standardfor medical electrical leads, for example. Additional apertures such asapertures 20 may be provided to couple to additional circuit componentsin a manner to be discussed below. Core element may further have one ormore guide members shown as guide members 21 and 23 integrally formed onthe surface of core element 2. These guide members serve as support andpositioning mechanisms for the additional circuit components, and alsoimproves the overmolding process, as is described below.

FIG. 1 further illustrates a circuit member 40 which is formed of aconductive material such as stainless steel, titanium, niobium,tantalum, or any other conductive biocompatible conductive material.Circuit member 40 includes multiple conductive traces or finger elements42 through 52, each extending to a respective connector pads 53 through57. When the circuit member 40 is initially coupled to core member 2,connector pads may be electrically and mechanically joined to make theassembly process more efficient. Circuit member 40 may be soldered orwelded to the various metal piece parts associated with core element 2,including set-screw blocks 10 and 12, and the various connector members30 in a manner to be discussed below.

As noted above, using a single circuit member 40 having conductivefinger elements that are mechanically and electrically joined makes theinitial assembly process easier since multiple elements need not beloaded onto the core element 2. However, in this embodiment, anadditional step is required later in the assembly process toelectrically isolate these components, as will be discussed below. Inanother embodiment, each of the multiple conductive finger elements 42through 52 may be an individual circuit element that is not mechanicallyor electrically coupled to the other finger elements. In thisembodiment, the multiple finger elements must be individually loadedonto the core element. However, the additional step of electricallyisolating these components later is not required. In yet anotherembodiment, the conductive finger elements may be joined in a singlecircuit member via insolated material. In this embodiment, the circuitmember is a unified structure that couples the conductive fingerelements mechanically, but provides electrical isolation. In thisembodiment, the additional step of electrically isolating thesecomponents later is not required.

In yet another embodiment, the circuit member 40 could be integrallyformed to include the various connector members and set-screw blocks sothat the soldering or welding process may be eliminated. Using thisembodiment, attaching the circuit member 40 to the core element involvesloading the receptacles and apertures of the core element with theset-screw blocks and connector members, respectively.

FIG. 2 is a front perspective view of core member 2 with respectiveset-screw blocks inserted into receptacles 4, 6 and 8, and withconnector members 58 and 30 inserted into circular receptacles 24 and26. This view further illustrates circuit member 40 coupled to coremember 2. In this embodiment, finger elements 48 and 50 of circuitmember may extend through apertures provided within core element 2. Forexample, finger element 50 is inserted through aperture 20, which is achannel that extends through the core member. Similarly, finger element48 extends through an additional aperture (not shown in FIG. 2) toposition circuit member in a precise location with respect to coreelement 2. In one manner of use, finger elements 48 and 50 are formed ofa material that is deformable, and which may be temporarily straightenedto be threaded through a respective aperture such as aperture 20. Inanother exemplary embodiment, finger elements 48 and 50 are initiallystraight, and may be manually or automatically bent in the manner shownin FIG. 2 after being inserted within a respective aperture.

After circuit member 40 is coupled to core member 2, it may be solderedor welded to form predetermined electrical and mechanical connectionsbetween connector members and set-screw blocks and respective ones ofthe conductive finger elements. For example, finger element 46 may becoupled to set-screw block 10, whereas finger element 48 is electricallycoupled to set-screw block 60.

Additional circuit elements may further be coupled to the core elementusing soldering, welding, or any other appropriate process. For example,jumper 62 may be soldered or welded to both finger element 46 andconnector member 58 to form an electrical connection between the twocomponents. Jumper 66 may be positioned on the surface of core member 2using guide members 21 and 23 to align the circuit member in a desiredlocation so that an electrical connection may be formed betweenset-screw block 12 and a predetermined respective one of the fingerelements.

FIG. 3 is a back perspective view of an alternative embodiment of thecore member designated core member 2 a. Although similar in almost everyrespect to the core members of FIGS. 1 and 2 discussed above, this coremember includes a support structure 70 that is integrally molded intocore element 2, and which is provided to receive and support connectormembers such as connector members 30 and 58. This support structure hasa cutaway portion 72 to allow circuit element 62 to be welded orsoldered to connector member 58. Although this support structure helpsmaintain the connector members in position during the second-shotovermolding process, it may make insertion of the connector members morecumbersome, and adds additional mass to the core element 2, which may beundesirable for reasons to be discussed further below.

FIG. 3 further illustrates the manner in which finger elements 48 and 50of circuit member 40 are threaded through apertures of core member 2.Further illustrated is circuit element 66, which is maintained inposition on the surface of core element by guide members 21 and 23 toform an electrical connection between set-screw block 12 and fingerelement 42.

FIG. 4 is a bottom perspective view of core member 2. This viewillustrates the manner in which finger elements 48 and 50 extend throughapertures 20 and 64, respectively. This view also shows the manner inwhich the various finger elements may be electrically coupled toconnector members and set-screw blocks. For example, finger element 44is jumpered via circuit element 70 to set-screw block 72; finger element46 is electrically coupled to set-screw block 10, and so on.

As shown in FIG. 4, one manner of retaining circuit member 40 inposition in proximity to core element 2 is through the use of aperturesthat extend through the core member and are adapted to receiverespective finger elements of the circuit member 40. While this helps toprevent shifting of the circuit member 40 during the second-shot moldingprocess, the process of threading the finger members through the variousapertures is cumbersome and time-consuming.

FIG. 5 is side perspective view of an alternative embodiment of thecircuit member. In this view, like features of circuit member 40 b ascompared to circuit member 40 of FIGS. 1 through 4 are designated withlike numeric identifiers including an additional suffix. This embodimentincludes finger elements 44 b through 46 b that are not adapted toengage apertures in a core element. Instead, these elements are adaptedto be placed externally on the surface of the core element to reduceassembly time prior to the second-shot overmolding step. One or more ofthe finger elements such as finger element 42 b may have a longer,flexible conductive end. This end is adapted to be manually shaped toconform to a surface of the core member, as described below. FIG. 5 alsoillustrates the use of alignment apertures 90 and 92, which are providedto position the core element at a predetermined location within thesecond-shot mold to be discussed below.

FIG. 6 is side perspective view of an alternative embodiment of the coreelement adapted to engage the circuit member 40 b of FIG. 5. As in FIG.5, like features of core element 2 b as compared to core element 2 ofFIGS. 1 through 4 are designated with like numeric identifiers includingan additional suffix. Core element 2 b includes channel guides such aschannel guides 100 through 110 that are provided to guide the fingerelements of circuit member 40 b into the desired position on the surfaceof core element 2 b. During the second-shot overmolding process, thesechannel guides retain the finger elements in position, and preventshifting that may results in shorts between adjacent finger elements.These channel guides also promote integration of the material of thecore element with the additional thermoplastic material provided duringthe overmolding process, as will be discussed further below.

FIG. 7 is a side perspective view of circuit member 40 b positioned onthe surface of core element 2 b. This figure illustrates the manner inwhich finger elements are positioned using the guide members. Forexample, finger element 50 b is positioned between guide members 104 and106, and finger element 42 b is positioned between guide members 108 and110 provided on the bottom surface of core member 2 b. The fingerelements may be soldered or welded to the conductive components such asthe set-screw blocks that are inserted in core member 2 b in the mannerdiscussed above. Other circuit elements may also be used to formelectrical connections between circuit member 40 b and a predeterminedconductive component. Alternatively, the longer finger elements such afinger element 42 b having a flexible elongated end 42 c (FIG. 5) may bemanually shaped into position and welded to form the desired connectionas shown in FIG. 7. In this example, the end 42 c of finger element 42 bis shaped along the top surface of core member 2 c to electricallycouple to set-screw block 12 c. This use of longer conductive fingerelements makes the assembly process more efficient by eliminating theneed for additional circuit components, and by minimizing the number oflocations that must be welded or soldered.

After all conductive components have been inserted into the core elementand the circuit member 40 b has been welded, soldered, or otherwisefixed into place, the resulting core element assembly may be prepared toundergo the second-shot overmolding process. This preparation mayinvolve inserting pin members into the connector members and theapertures of the set-screw blocks so that thermoplastic material doesnot fill these structures during the overmolding process. FIG. 7illustrates pin members 120 and 122 being inserted into connectormembers 58 b and 30 b, respectively. Pin members 124 and 126 aresimilarly inserted into lead bores 29 b and 28 b, respectively.Additional pin members or bushings (not shown in FIG. 7 for clarity) maybe inserted into the apertures of each of the set-screw blocks of coreelement 2 b. These pin members are made of a material that willwithstand the temperature and pressure conditions associated with theinjection molding process. For example, the pin members may be made of atool steel or another type of stainless steel. In one embodiment,multiple ones of the pin members may be incorporated into a coreassembly structure to make insertion into the core element easier.

FIG. 8 illustrates an exemplary lead core assembly 130, which isassembly that provides the pin members 120 through 126 shown in FIG. 7.The lead core assembly aligns the pin members, and allows them to beinserted in one step.

In an alternative embodiment, ones of the pin members such as thoseinserted into the set-screw blocks may be eliminated by usingprotrusions in the second-shot mold assembly. These protrusions areinserted into the set-screw blocks as the core element is placed withinthe mold and the mold is closed, thereby eliminating the step ofmanually inserting the pin members into the core element. This isdiscussed further below.

FIG. 9 is a perspective view of a core element being prepared for theovermolding process. This view, which is similar to that shown in FIG.3, illustrates core member 2 a and the associated metal piece parts thathave been loaded into the core member. Lead core assembly 130 isutilized to insert pin members 120, 122, 124, and 126 into therespective structures of the core element as discussed in reference toFIG. 8. Similar bushings 140, 142, 144 and 146 may be inserted into theapertures of the set-screw blocks. As noted above, bushings 144 and 146may be eliminated by instead providing protrusions within cavity 148 ofthe bottom portion 150 that are aligned with the set-screw blocks.Similar protrusions may be provided in the top portion 172 of the moldto replace bushings 140 and 142. Providing such structures in the molditself eliminates the requirement of manually loading the bushings intothe core element.

After the core element is prepared for the overmolding process, theentire assembly may then be loaded into cavity 148 of a bottom portion150 of a second-shot mold fixture. The lead core assembly is positionedwithin the mold as shown by dashed lines 152 and 154. In this position,the lead core assembly suspends the core element within the cavity ofthe mold so that the surface of the core element is not in contact withthe interior surface of the mold. The positioning of the core assemblymay further be aided by fitting predetermined ones of the aperturesincluded in the circuit member 40 with the alignment pins 160 and 162 ofthe mold as illustrated by dashed lines 164 and 166. For example, theapertures in connector pads 54 and 56 of circuit member 40 (FIGS. 2 and3) or the alignment apertures 90 and 92 (FIG. 5) could be used for thispurpose. The circuit member 40 may further be supported by a shouldermember 170.

After the assembly has been properly aligned within the bottom portion150, the top portion 172 of the second-shot mold fixture is aligned withthe bottom portion. This may be accomplished by inserting pegs 174 and176 into channel members 178 and 180. Both top and bottom mold portionsmay include additional channels such as channels 182 and 184 toaccommodate set-screws 140 and 142, respectively. Similar channels maybe provided in the bottom portion 150 of the mold fixture.

When the bottom and top portions of the mold fixture have been aligned,a press may be utilized to maintain the alignment during thehigh-pressure injection procedure. A thermoplastic material is heated toat least the melting temperature, or preferably, slightly above themelting temperature, of the material, and is injected into cavity 148via injection port 190. The same, or a different, thermoplastic materialmay be used in the second-shot injection process as compared to thatused in the core element. Moreover, the second-shot material mayentirely encapsulate the core element, or alternatively, need only covera portion of the core element. For example, it may be desirable to leaveexposed a portion of the thermoplastic material included in the coreelement in the region of the circuit member connector pads.

During the second-shot injection process, it is important to ensure thatbonding occurs between the core element and the second shot material. Ifbonding does not occur, very small amounts of ionic liquid pool betweenthe core element 2 and the overmold material after the connector hasbeen implanted within a living body for an extended period of time. Thismay result in what is an unacceptably large leakage current betweenadjacent finger elements of the circuit element. One way to ensure thatadequate bonding is achieved is to heat the second-shot plastic as hotas the material characteristics will allow, and to inject the materialas quickly as possible. This allows the core element to be heated by,and thereafter bonded to, the second-shot material.

Another method used to enhance the bonding process is to ensure that themass of the core element is as small as possible. This allows the coreelement to be heated sufficiently during the overmold process. In oneembodiment, the mass of the thermoplastic material incorporated into thecore element is less than half of the mass of the material utilizedduring the overmold process, and is preferably less than thirty percentof that of the overmold structure.

Another mechanism for enhancing the bonding of the core element to theovermold material involves heating the core element prior to injectingthe second shot of thermoplastic material. If this method is utilized,the mass of the core element may be greater while still achievingadequate bonding. This is because the second shot of thermoplasticmaterial is not providing all of the heat needed to warm the coreelement, with at least some of the heat being provided during theheating step that precedes the injection step. In one embodiment, themass of the core element is greater than fifty percent of thethermoplastic material used during the overmold process while stillretaining adequate bonding.

Integration of the core element with the overmold material may befurther enhanced by providing relatively thin protruding structures tothe core member surface. Because these relatively thin structures arereadily melted and integrated with the second-shot material, integrationof the core element with the overmold structure is enhanced. Forexample, guide members 100 through 110 (FIG. 6) serve not only to guidecircuit elements on the surface of the core member, but also facilitatethis type of bonding between the core element 2 and the overmoldmaterial. In one embodiment, additional thin fin-like structures may beprovided in arbitrary shapes along various surfaces of the core memberto facilitate additional integration. Such structures may be included inthe first-shot mold assembly. Although such structures do enhanceintegration, the addition of such structures makes the molding of thecore element more complex.

Following the injection of the overmold material, the entire assembly isallowed to cool for twenty to seventy seconds, depending on the type ofthermoplastic material utilized as determined by the manufacturerspecifications. The top portion of the mold is removed from the bottomportion, causing the finished connector assembly to be released. Afterremoval from the mold, the connector pads of the circuit member 40 maybe separated, if necessary, to achieve electrical isolation, as may beperformed by cutting away the intervening conductive traces. The padsmay then be soldered or welded to respective connectors of animplantable medical device such as a pacemaker orcardioverter/defibrillator, and overlaid with a medical adhesive tomaintain electrical isolation in the connection area. It may be notedthat if individual circuit elements are utilized in place of circuitmember 40 or 40 b, the step of removing the intervening conductivetraces between finger elements may be eliminated.

As discussed in the foregoing paragraphs, one way to promote theformation of an adequate bond between the core member and the overmoldmaterial is to utilize a core element that is as small as possible. Analternative embodiment of a core element directed to minimizing coreelement mass is shown in FIG. 10. It may be noted that in thisembodiment, the walls defining receptacles 4 c, 6 c, and 8 c arerelatively thin structures as compared to similar structures shown inFIGS. 1 and 6. Other structure adjacent to receptacle 8 c has also beeneliminated.

FIG. 11 is a perspective side view of an exemplary connector assemblyformed after injection of the second-shot material. The side view ofFIG. 11 corresponds to the view of core element 2 b in FIG. 6. Circuitmember 40 has been trimmed in the manner discussed above to achieve thenecessary isolation between pads. This view further illustrates anadditional bore 190 extending through the second thermoplastic material191, which may be integrally formed by a protrusion provided within thecavity of the bottom portion 150 or top portion 172 of the mold. Thistype of bore is provided to allow for tightening of the set-screws aftera lead is insert into a respective lead receptacle such as receptacle200 in this instance. This bore will be fitted with a stop member suchas a grommet and/or a washer to form a fluid-tight opening that isadapted to receive a tool used during the tightening of the set-screw tothe lead pin or ring connector. In one embodiment, other apertures 202 aand 202 b are provided to allow the connector to be sutured to tissuewithin the implant cavity. This type of aperture may be formed by a pinthat extends between the bottom portion 150 and top portion 172 of themold assembly.

FIG. 12 is an alternative embodiment of the second-shot mold assembly ofFIG. 9. This view illustrates core element 2 a, the associated metalpiece parts that have been loaded into the core member, and circuitmember 40. This loaded core element assembly is then positioned in thebottom portion 150 a of the second-shot mold fixture. In a mannersimilar to that discussed above with respect to FIG. 9, aperturesprovided within the circuit element may be positioned over pins 203 and204 of shoulder member 205 to properly align and suspend core memberover cavity 206 of the mold. Two slidable members 207 and 208 areprovided to move into position around the core element assembly, asshown by arrows 209 and 210, respectively. These slidable members may beadapted to slide within tracks of the bottom portion 150 a. Each of theslidable members includes one or more pegs such as pegs 211 and 212 ofslidable member 207 to engage the set-screw block apertures so thatadditional bushings 140 through 146 (FIG. 9) are not needed. Theslidable members provide additional stability during the second-shotinjection mold process, and make removal of the connector assemblyfollowing the second-shot injection process less difficult.

Also shown in FIG. 12 is lead core assembly 130, which may be slidablypositioned within the bottom portion 150 a of the mold as illustrated byarrow 211 to engage the connector members of the core element 2 a in themanner discussed above. Once the lead core assembly 130 and slidablemembers 207 and 208 are in position, a top portion of the mold which issimilar to top portion 172 (FIG. 9) may be positioned over the bottomportion 150 a. This top portion is held in position by a press or othermechanism during the second-shot injection process, as discussed above.

FIG. 13 is a flowchart indicating the steps utilized to make the currentexemplary connector assembly. Although for discussion purposes theassociated description involves the core element of FIG. 1, it will beunderstood the described process is equally applicable to the productionof any connector type, or an entirely different type of thermoplasticcomponent. In step 220, core member 2 is created. This may beaccomplished by injecting a thermoplastic material into a primary moldassembly, or by fabricating a core member such as by a machiningprocess. In step 222, the core member is loaded with the variousconductive components such as the set-screw blocks and connector membersto form the core member assembly. This step includes welding or solderthe circuit member 40 to the various other conductive components.Processing continues with step 224, wherein the core member assembly isloaded onto the lead core assembly. Additional bushings may be insertedinto set-screw blocks in 226 to ensure these structures remain openduring the overmolding process, although this step is unnecessary ifprotrusions adapted to be inserted in the set-screw blocks are includedin the second-shot mold assembly.

Next, in step 228, the core member assembly is loaded into the bottomportion 150 of the second-shot mold assembly. If desired, apertures inthe circuit member 40 may be used to align the core member assemblywithin the mold cavity in a manner discussed above. The top portion 172of the mold assembly is positioned over the bottom portion 150 asindicated by step 230, and the two portions are held together using apress, for example. Processing continues with step 232, wherein thethermoplastic material is injected to create the overmold. To bond thecore member 2 with the overmold material, it is critical to heat thecore member adequately. This may be accomplished by ensuring the mass ofthe core member is as small as possible as compared to the mass of theovermold material. In one embodiment, the mass of the core element isless than fifty percent of the mass of the overmolding material, and ispreferably less than thirty percent of the overmold mass, as isdiscussed above. The bonding process may further be enhanced bypre-heating the core element prior to the overmold process, or byutilizing a thermoplastic material that can be heated to a relativelyhigh temperature without altering the material characteristics. Ineither of these instances, the core element may have a mass that isgreater than fifty percent of the overmold process while still achievingadequate bonding.

The connector assembly is cooled in step 234, and then removed from themold assembly in step 236. The lead core assembly and optional bushingsmay be removed in step 238, and the various connector pads of thecircuit member may be electrically isolated, as by removinginterconnecting ones of the conductive traces. This is illustrated instep 240. As noted above, if individual circuit elements are used, thisstep is not needed.

FIG. 14 is a side perspective view of a completed connector assembly 248which is similar to that shown in FIG. 11. Connector assembly 248 iscoupled to an implantable medical device (IMD) 250, which may be apacemaker, cardio/defibrillator, neurological pain stimulator, or anyother type of implantable medical device utilizing medical electricalleads. In one embodiment, the connector pads such as pads 252 through258 of the connector assembly 248 are welded or soldered to afeedthrough pattern of the IMD. This provides the desired electricalconnections between the connector assembly and the IMD.

Although the above description discusses a particular type of connectorassembly adapted to couple to four leads having particular types ofconnectors, it may be noted that the inventive process may be adapted tomanufacture any type of connector assembly having any number of shapesand sizes, and that is adapted to couple to any type of lead connector.Alternatively, the process could be utilized to manufacture any othertype of thermoplastic component that is adapted to include conductivepiece parts. Thus, the description of the specific connector assemblyset forth above should be considered merely exemplary in nature.

1. A circuit assembly adapted to be implanted within a living body,comprising: a core element formed of a thermoplastic material; at leastone circuit element capable of conducting electricity positioned inproximity to the core element; a connector member to couple electricallyand mechanically to a ring connector of a lead; a receptacle formed inthe core element for receiving the connector member therein; and a guidemember integrally formed on a surface of the core element to support andposition the at least one circuit element on the surface of the coreelement.